1. Technical Field
The present invention relates to an apparatus and method for forming tubes of dough. Specifically, this invention relates to a dough-rolling apparatus having a dough sheeter, a receiving conveyor having a ramped section, a roll-initiating curtain, and a roll-completing curtain.
2. Description of Related Art
Rolled products are found in many different food industries such as croissants, wafer sticks, and frozen/stuffed taquitos. Many prior art processes have been developed to address the complexities of rolling each of these products. For example, the croissant industry generally utilizes a relative speed differential between two belts. The croissant industry uses relatively thick dough with a high degree of tackiness, which makes it fairly easy to manipulate. In contrast, the wafer stick industry typically uses a batter that is drum dried, wound around a mandrel at a 45-degree angle, and then cut into pieces.
In the snack food industry, however, the dough used typically comprises one or more starches and/or flour, which dough is then thinly sheeted, cut into pieces, and then toasted, fried and/or baked. Typical dough types include, but are not limited to, the following: potato, rice, corn-based doughs, and wheat-based doughs. It is particularly desirable to produce a cylindrically shaped snack piece made of thinly sheeted dough that is toasted, fried, and seasoned. The dough used in such snack products, unlike the dough used in other food industries, is generally very thin, fragile, and difficult to manipulate. This makes typical rolling technology unacceptable for such an application. Additionally, the processing rates required in the snack food industry are very high relative to other industries, making dough-rolling even more difficult.
Although hanging curtains have been used in the prior art to roll dough sheets, existing prior art devices suffer from less-complete rolling of product when dough sheets fail to separate from the conveying surface upon meeting such hanging curtains. Furthermore, prior art dough-rolling devices lack the ability to produce rolled products from thin dough pieces reliably, efficiently, and at high volume and high speeed. For example, while the Rodriguez patent (U.S. Pat. No. 6,393,974) discloses the use of hanging curtains over flat conveyors, there has never been a ramped dough-rolling apparatus to enable more reliable, complete rolling. U.S. Pat. No. 6,393,974 B1 (the “'974 Patent”), titled “Apparatus for Production of a Small Tortilla,” is directed towards an apparatus for rolling raw tortillas into the shape of a taco and contains one independent claim (claim 1). The '974 Patent relates to a dough-rolling apparatus having a “pre-rolling up mesh” and a “final rolling up mesh,” and it repeatedly emphasizes the need for such meshes to be positioned over an “acceleration conveyor” that operates faster than the preceding “exit conveyor.” For example, the '974 Patent at column 4, lines 53–55, states that “[n]ext to the exit conveyor 106 is an acceleration conveyor 108 with an equal transversal section that advances at a greater speed than the exit conveyor 106.” At column 5, lines 6–14, the '974 Patent continues, “pre-rolling up meshes 119 are placed with a small surface of contact and dragging with the mesh of acceleration conveyor 108 . . . The final rolling up meshes 120 show a greater surface of contact and dragging with the acceleration conveyor 108 . . .” Operating and maintaining an acceleration conveyor in addition to a sheeter exit conveyor is undesirable, as it introduces another potential product transfer point where problems may occur. Adding a second conveyor of a different operating speed to the system can also increase the complexity of the control process and add capital expense. The '974 patent also states in column 1, lines 58–63: “adjustment of the speed of the exit conveyor together with modifications to the rollers is required. The new structure of the laminator eliminates the versatility of such conveyor and renders the laminator incapable of being used afterwards as other types of products requires speeds by which the laminator was redesigned.”
Another prior art dough-rolling apparatus is disclosed in U.S. Pat. No. 6,171,628 B1 (the “'628 Patent”), which issued to Ueno on Jan. 9, 2001 and is titled “Method for Rolling Up a Sheet of Dough.” Although the '628 Patent discloses the use of hanging curtains to induce sheets of dough to roll, the '628 Patent actually teaches away from the use of hanging curtains and is instead directed towards a roll-up roller for rolling sheets of dough. See '628 Patent at column 1, lines 38–40; '628 Patent FIGS. 7a, 7b and 7c (illustrating common jamming problems associated with dough-rolling curtains).
U.S. Pat. No. 6,079,970 (the “'970 Patent”) issued to Ueno on Jun. 27, 2000, and is titled “Apparatus for Rolling Up a Sheet of Dough.” Like the later-issued '628 Patent, the '970 Patent actually teaches away from and discourages the use of hanging curtains and is instead directed towards a roll-up roller for rolling sheets of dough. See '970 Patent at column 1, lines 35–37; '970 Patent FIGS. 7a, 7b and 7c. 
U.S. Pat. No. 4,994,293 (the “'293 Patent”) and U.S. Pat. No. 4,905,583 (the “'583 Patent”) were granted to Hayashi on Feb. 19, 1991 and Mar. 6, 1990 and are titled “Method for Rolling Croissant Dough Pieces” and “Apparatus and Method for Rolling Croissant Dough Pieces,” respectively. The '583 Patent and the '293 Patent, which is a divisional application of the '583 Patent, are both directed towards an apparatus and method for rolling triangular dough pieces into croissant shapes using a flexible hanging screen. The '293 and '583 Patents emphasize that the dough pieces are to be stretched and transferred to a rolling apparatus without significantly decreasing the adhesiveness of the dough pieces. Whereas prior art methods for rolling dough pieces into croissant shapes employed the use of flour to make dough pieces less adhesive and more easily managed, the '293 and the '583 Patents teach that such loss of adhesiveness is disadvantageous for producing tightly-wound croissants. The '293 and '583 Patents, however, do not provide a means for ensuring that the dough-rolling curtain effectively initiates a rolling action, nor do they offer solutions to the problems of effecting more complete rolling and preventing product jamming along the flat surface of the dough-rolling conveyor. While it is possible to use a single dough-rolling curtain to roll a piece of sheeted dough, such a device tends to have lower rolling efficiency and lower throughput than is desirable.
U.S. Pat. No. 4,666,391 (the “'391 Patent”) was granted to Watt et al. on May 19, 1987 and is titled “Apparatus for Rolling Up a Pastry Layer and a Separator Sheet.” The '391 Patent is directed towards an apparatus for forming rolled pastries having a film interposed between adjacent rolled layers to inhibit the layers from sticking to each other. While the '391 Patent discloses the use of a single drag-inducing member as a roll-up device over a flat conveying surface, the '391 Patent does not address the problem of jamming, which occurs when sheeted dough fails to separate from the conveying surface upon meeting the drag-inducing member.
U.S. Pat. No. 4,389,176 (the “'176” Patent) was granted to Nenci on Jun. 21, 1983 and is titled “Machine for the Production of Tubular Casings of Alimentary Dough.” The '176 Patent relates to a dough-rolling device in which pieces of dough are rolled around support cores to form cannoli tubes. While the '176 Patent discloses the use of a metal mesh screen as a dough-rolling device, the metal mesh of the '176 Patent is supported and held taught between two rollers. See '176 Patent at column 6, lines 26–30. A taught, flat mesh screen would not be appropriate for thin and fragile doughs such as thinly-sheeted corn masa, because such a flat screen may unduly concentrate rolling forces and pressure at the minimal contact area between the flat screen and rolled masa products. This would likely result in destruction of the fragile masa product. Thus, a flexible chain or mesh curtain is critical for rolling fragile dough pre-forms.
Consequently, a need exists for a dough-rolling apparatus and method that separates the leading edge of sheeted dough from the conveying surface before rolling for improved rolling consistency and to allow rapid changeovers to form traditional, flat products such as tortilla chips. In particular, such a dough-rolling apparatus should comprise a single conveyor having a ramped section leading to a roll-initiating mesh curtain and followed thereafter by a roll-completing mesh curtain. The ramped section of such an apparatus should provide: 1) improved rolling efficiency and completeness of rolling; 2) greater throughput and faster speeds; and 3) reliable, consistent rolling performance even when other pieces of equipment within the rolling system are not operating within the desired conditions, or when wearable parts begin to wear or undesirably collect product. The ramped section of such an apparatus should also have a launching-side angle and a declining-side angle that is optimized for the speed of the conveyor and offers an appropriate balance between the curtain rolling forces and the friction applied by the conveyor. Otherwise, too little ramp angle may result in incomplete or lesser degrees of rolling, while too much ramp angle may not offer enough conveyor surface friction and thus cause product to fall back and possibly jam the apparatus. An improved dough-rolling apparatus should also employ replaceable wear strips and a lift-arm assembly for quickly repairing or replacing hanging curtains, or for changing over to standard processes such as, but not limited to, tortilla chip processing. A lift-arm assembly enables quick changeovers of replaceable, wearing parts with less downtime. An improved dough-rolling apparatus should further include a stiff plate or other stiff supporting members for the conveying surface directly under the rolling curtains to ensure a flat surface across the width of the conveying surface. Such a dough-rolling apparatus should also include a sheeter and cutter, upstream from the rolling stage, having an improved dough-cutting pattern for cutting sheeted dough into pieces (pre-forms) that have shapes and orientations advantageous for rolling.